More specifically, the invention relates to a drum brake comprising at least: a drum; two shoes in the shape of arcs of a circle, arranged facing an internal face of the drum and carrying respective friction linings; an actuator inserted between the shoes and operated selectively to make the shoes move, in a centrifugal movement towards the internal face of the drum; a spring connecting the shoes to move them closer together, in a centripetal movement counter to the centrifugal movement as soon as the actuator is no longer being operated; a rocking lever carrying an adjustment blade and which moves in a back and forth angular movement consisting of two pivoting movements in opposite directions, correlated with the centrifugal and centripetal movements of the shoes; an adjustable-length strut inserted between the shoes to limit their centripetal movement, and comprising two threaded elements forming a screw-nut connection, the length of this strut being adjusted by unscrewing the screw-nut connection as the friction linings wear; and a toothed wheel secured to one of the elements of the screw-nut connection and selectively rotated by the adjustment blade during a first of the pivoting movements of the rocking lever, the adjustment blade extending, lengthwise, transversely with respect to the toothed wheel, developing widthwise in a mean plane parallel to the first pivoting movement, and interfacing with the toothed wheel, during the first pivoting movement, rather more tangentially than radially.
This type of drum brake is well known to those skilled in the art and is, for example, illustrated in U.S. Pat. No. 4,502,574 the teaching of which is incorporated into this description.
Despite their attraction as a result of the simplicity of their structure, such brakes sometimes tend to lock when subjected to an excessive actuating force, particularly if they have been used in extreme conditions which have led to a significant rise in temperature.